1. Field of the Invention
The invention concerns a drive system, especially for a motor vehicle, and a method of operating same.
2. Description of the Related Art
Basically, the transmission of force in motor vehicles--which is responsible for the forward movement of the vehicle--depends on drive slip between tires and road. In general, the starting and acceleration processes occur at low slip values, during which an increase in slip also produces an increase in the useable force closure at first. As it continues to increase, however, the force closure is again reduced, so that an excess drive torque becoming larger under corresponding acceleration leads to a fast rise in rotary speed of a drive wheel or the drive wheels.
A regulating of the drive slip, i.e., a so-called drive slip control (ASR), prevents such a spinning of the drive wheels and regulates the drive slip down to permissible values. Such drive slip controls are known in the state of the art (see, for example, "Automotive Handbook," publisher: Robert Bosch GmbH, Dusseldorf, 21st Ed., 1991, pp. 555-559).
Regulation of drive slip--in the state of the art--is accomplished in that the driving moment is reduced upon reaching a limit value of drive slip or a change in the drive slip over time (time derivative). Reduction of the drive torque is accomplished either by adjustment of the engine, i.e., by throttle valve adjustment or by ignition time adjustment, or by activating one or more wheel brake(s). A combination of both measures is also known. In particular, in addition to the engine adjustment, which occurs when exceeding a first limit value of the drive slip, the wheel brakes can be activated when a second, higher limit value of drive slip, is attained.
The drawback to these known drive slip controls is that, first, the engine adjustment is slow and sluggish and, secondly, the overall drive slip control is hard to manage, i.e., it is almost never possible to achieve a particular decrease in drive torque over time.